1. Field of the Invention
This invention relates to transmitters and receivers of electromagnetic energy. More specifically, it relates to improved transmitters and receivers that provide an indication of the angle of incidence of electromagnetic energy in a plurality of fields of view. While the present invention is described herein with reference to particular embodiments, it should be understood that the invention is not limited thereto. The present invention may be adapted and employed for a variety of electromagnetic requirements as those skilled in the art will recognize in light of the present disclosure.
2. Description of the Prior Art
Conventional techniques for obtaining the azimuth or angle of incidence of optical or other electromagnetic energy typically utilized either an array of directional detectors or a single directional detector adapted to rotate through the target plane.
The array approach requires the use of a plurality of highly directional receivers. Each receiver is assigned to a section of the area to be scanned. In an optical system, each receiver would include a photodetector and an associated electronic circuit so that any optical energy detected by the receiver would be electrically interpreted as coming from a predetermined direction.
Obviously, this approach can be costly where accurate angle determinations must be made. That is, the cost/performance of such a system would depend on the number of detectors or receivers required. Moreover, no matter how many receiver elements are utilized, accuracy would be limited by the inherent shortcomings of a discreet system. That is, it is impossible to determine where the image is within the assigned sector.
These shortcomings can be avoided somewhat by utilizing a rotating receiver approach. Here a highly directional receiver element is mounted for rotation so that a single receiver element can scan the desired area. This technique can be somewhat more accurate than that of the dedicated array insofar as the exact angle at which the element is pointed is known. However, the rotating element approach suffers from limitations common to mechanical systems, i.e., speed and durability. The response time of a system utilizing this technique would be much longer than that of the dedicated array. Actual response could be improved somewhat by using several receiver elements, however, where ultra fast response is required, this solution may be too costly.
A third approach calls for the utilization of linear detector arrays with complicated lenses having a fairly high resolution over large fields of view. Such lenses are currently so expensive too to be cost effective for most conventional applications.
One solution to these problems has been provided by an invention disclosed in Applicant's copending application entitled "Apparatus for Determining Angle Incidence of Electromagnetic Energy", Ser. No. 155,887, now U.S. Pat. No. 4,325,633. There an element is provided which is adapted to transform incoming electromagnetic energy to a line image having a radiant power distribution along its length which is peculiar to the angle of incidence thereof. The power distribution of the line image is then measured by a detector to provide an electrical signal proportional to the angle of incidence.
While the invention described in the copending application provides a simple, accurate and inexpensive solution to the above mentioned prior art systems, the element provided is capable of detecting electromagnetic energy in only a single field of view. As a result, in applications where it is desirable to have two or more fields of view, a detector must be provided for each field of view required, e.g. where two sets of data are required as for target orientation, or velocity or in a range sensing application where system attitude and flight direction are to be determined. It is evident that as the number of fields of view required increase, the cost and complexity of the system increases accordingly. It is therefore desirable to provide transmitters and receivers capable of radiating and detecting electromagnetic energy in a plurality of fields of view using a single element.